Abstract
The hydrothermal stability of 1-D medium pore zeolites ZSM-22 with different nominal Si/Al ratios (30, 46, 80, and 100) was investigated in hot liquid water environments at different temperatures (100, 150, 200, and 250 °C) and different exposure times (6, 12, 36, 72, and 144 h). The changes in the zeolite structure, phase transformation, and textural properties were characterized by X-ray diffraction, scanning electron microscopy, 27Al and 29Si magic-angle spinning nuclear magnetic resonance, temperature-programmed desorption of ammonia, IR spectra, and X-ray fluorescence. After the treatment in a hot water environment, TON framework suffered from desilication (silicon extraction), phase transformation, and crystallinity change. The degree of desilication via siloxane hydrolysis is dependent on the treatment time and temperature. At high temperature (250 °C), severe desilication, textural properties degradation, and formation of extra-framework Al species (EFAL) were observed. This formed EFAL worked as ...
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